extend_trtab: allow identical trfuns to be overwritten;
extend_trtab: allow identical trfuns to be overwritten;

MerelyAPseudonym/isabelle,MerelyAPseudonym/isabelle,MerelyAPseudonym/isabelle,MerelyAPseudonym/isabelle,MerelyAPseudonym/isabelle,MerelyAPseudonym/isabelle